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Washington (CNN) -- Much remained up in the air Tuesday, the biggest single day of the Republican presidential race, with each of the four remaining candidates hoping for game-changing victories after months of fierce campaigning.
The momentum heading into Super Tuesday, when voters in 10 states will weigh in, clearly is with former Massachusetts Gov. Mitt Romney. He has won the last four states, and scored recent endorsements from conservative stalwarts such as former U.S. Attorney General John Ashcroft, House Majority Leader Eric Cantor of Virginia and Sen. Tom Coburn of Oklahoma.
And yet momentum has been fleeting, at best, in the GOP nominating contest. Romney was anointed the man-to-beat after winning New Hampshire (and Iowa, until updated results awarded that state to former Sen. Rick Santorum) before falling in South Carolina. He soared to that perch again after taking Florida, then saw Santorum win three straight states.
Like much else in this race, what happens next is anyone's guess.
A CNN/ORC International poll released Monday showed a tie for the lead in Ohio. Both Romney and Santorum coming in at 32% among likely Republican voters, with the ex-governor gaining ground thanks to strong support by Catholic voters.
Former House Speaker Newt Gingrich had 14% support and Texas Rep. Ron Paul was at 11% in the same poll.
"The surprise is that the Catholic candidate, Santorum, is losing the Catholic vote," said CNN Polling Director Keating Holland. "Among Ohio Catholics who are likely to vote on Super Tuesday, 39% back Romney compared to 33% who support Santorum."
Three other Ohio polls released Monday showed similar results, with a statistical tie between Romney and Santorum at the top and Gingrich and Paul well back.
Ohio is one of the big prizes on Super Tuesday, with 63 delegates in what will be a battleground state in the November election against President Barack Obama.
Late polls also showed Romney and Santorum statistically tied at the top in Tennessee.
Another CNN/ORC poll showed good news in Georgia for Gingrich, who for a time was the darling of the GOP field but has struggled since winning South Carolina.
Gingrich, who represented Georgia's sixth congressional district for two decades, has 47% support among likely Republican voters in the state, compared to 24% for Romney, 15% for Santorum and 9% for Paul. The former House Speaker has acknowledged that he must win Georgia to keep his campaign going.
He is last in the delegate count, with 39, according to CNN's unofficial estimate.
After victories last week in Michigan, Arizona and Saturday, Romney has more than twice as many delegates as anyone else with 207. He's followed by Santorum at 86 and Paul, with 46. It takes 1,144 delegates to secure the Republican nomination.
Tuesday's vote could shake things up. Besides Ohio, citizens in Cantor's Virginia and Coburn's Oklahoma will participate in primaries, as will people Ohio, Georgia, Tennessee, Vermont and Massachusetts.
Idaho, North Dakota and Alaska, meanwhile, are holding caucuses. The latter state has been burdened by record-breaking snow -- which caused the roof of Anchorage's Abbot Loop Community Church, where an estimated 2,500 voters are expected to caucus, to collapse last Friday.
"We have been dealing with this snow all winter and what's already on the ground won't affect us," said Alaska GOP chairman Randy Ruedrich.
Gingrich, for one, is already looking beyond Super Tuesday. He called Monday for another debate -- what would be the 21st so far -- saying they'd give Republicans in upcoming primary states of Mississippi and Alabama a chance to learn more about the candidates.
The former House Speaker has helped his cause in several previous debates, which provided him with free media exposure against the better-funded Romney campaign.
"I don't think Romney can just hide behind millions of dollars of paid ads," Gingrich said. "He's got to come out in the open."
There was no immediate response from the other candidates.
Gingrich's strategy has been to conserve resources until Georgia, then try to attract support in other traditionally conservative Southern states in hopes of slowing Romney and outdueling Santorum for right-wing votes.
Still, he's not even on the ballot Tuesday in Virginia, nor is Santorum.
And the former Pennsylvania senator's campaign also was unable to meet eligibility requirements in some Ohio districts -- putting any delegates he wins in them in jeopardy.
On Monday, Santorum lamented the continuing battle with Gingrich for conservative support in the race against the more moderate Romney. He also took aim at Romney's health care law in Massachusetts, saying it was a model for the federal health care reform law that is reviled by conservatives.
"Not only did Governor Romney institute the first government health care system in this country with 'Romneycare.' Not only did he institute it at a state level, but he recommended to President Obama that he adopt 'Romneycare' as a template for 'Obamacare' and guess what? They did," Santorum said in Miamisburg, Ohio.
Romney, campaigning in Youngstown, rejected such criticism.
"Our plan dealt with the 8% of the people in my state that didn't have insurance," Romney said of the Massachusetts program, adding that Obama's law deals with everyone. "It is not just about the uninsured; it is about all of health care. It doesn't make health care better; it makes health care worse."
When a woman asked whether he would repeal the federal health care law, Romney responded to laughs, saying: "Why would I not?"
Paul told the CBS program "Face the Nation" on Sunday that he was targeting the Super Tuesday caucus states of Alaska, Idaho and North Dakota in his quest for delegates, despite being the only surviving candidate without a primary victory so far.
Asked if he was running to win the nomination or simply secure enough ballots to be a force at the Republican convention in August, Paul said his goal was both.
"I don't know why there has to be an either-or," Paul said. "If you're in a race to make a point or promote a cause, the best way to do that is to win."
Gingrich said Sunday that despite Obama's improving favorability ratings, Republicans were still poised to take the White House and the Senate in November.
"People take stock," Gingrich said. "The price of gasoline is becoming a genuine crisis for many American families. If it continues to go higher, it will crater the economy by August. People will have no discretionary income. As a result the president will go into the fall with very expensive gasoline, a weakening economy, a disastrously bad policy in the Middle East. I think that's a pretty big burden."
Last month, Obama ridiculed the strategy of focusing on rising gas strategy, mentioning a news headline that said the rising gas price has Republicans "licking their chops."
"Only in politics do people root for bad news," he said.
CNN's Tom Cohen, Greg Botelho, Kevin Liptak, Peter Hamby, Rachel Streitfeld and Paul Steinhauser contributed to this report.